Hormone is a substance, which is present in a trace amount in the blood of a living body and governs various physiological activities. Thyroid stimulating hormone (TSH), which is one type of thyroid hormone, is often measured in clinical sites in order to determine and/or grasp thyroid function. In a normal state, the thyroid gland is stimulated by thyroid stimulating hormone (TSH), and as a result, thyroxine (T4) is secreted. However, when thyroid function is decreased as in the case of Hashimoto's disease, T4 is not secreted although TSH is secreted. Accordingly, when a subject is suspected to have hypothyreosis, the subject's TSH level in blood needs to be measured.
However, since hormone such as TSH is present only in a trace amount in the blood, a reagent and an apparatus, which are capable of high sensitivity quantification, are required. With regard to immunodiagnostic reagents using an antigen-antibody reaction, examples of a method not involving a labeling reaction, namely, a non-labeling method, include: immunodiffusion, immunonephelometry and nephelometry, which utilize a precipitation reaction; and erythrocyte agglutination and a latex method, which utilize an agglutination reaction. On the other hand, examples of a method involving a labeling reaction, which is currently used, include enzyme immunoassay (EIA method), radioimmunoassay (RIA method), fluorescence immunoassay (FIA method), chemiluminescence immunoassay (CLIA method), and bioluminescence immunoassay (BLIA method). These methods are applied depending on the type or property of a substance to be labeled. As a method for measuring TSH, for example, JP Patent Publication (Kokai) No. 2009-85703 A describes a method for measuring TSH, which comprises using a commercially available antibody against human TSH, allowing TSH to come into contact with a carrier to which the aforementioned anti-TSH antibody has been bound, and then measuring an agglutination generated as a result of the aforementioned contact, wherein the method is characterized in that multiple types of anti-TSH antibodies, which recognize different TSH epitopes, are independently supported on individual carriers, and the thus obtained TSH antibody-supported carriers are then each allowed to come into contact with an analyte containing TSH on a time difference basis.
For the above-described immunodiagnosis of TSH, a TSH antibody is required. However, since a canine TSH (hereinafter also referred to as “cTSH”) antigen is present only in a trace amount in a living body, it is difficult to ensure a sufficient amount of canine TSH antigen used as an immunogen in the production of a canine TSH antibody. Moreover, at present, such a canine TSH antibody is not commercially available. Furthermore, since it is also difficult to construct an expression system of a recombinant canine TSH protein, it is difficult to obtain a large amount of canine TSH protein. As described above, since it is not possible to obtain a large amount of canine TSH protein, ordinary immunization cannot be conducted. As such, it has been difficult to produce an anti-canine TSH antibody.